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11 <div class="doc_title">LLVM 1.5 Release Notes</div>
14 <li><a href="#intro">Introduction</a></li>
15 <li><a href="#whatsnew">What's New?</a></li>
16 <li><a href="GettingStarted.html">Installation Instructions</a></li>
17 <li><a href="#portability">Portability and Supported Platforms</a></li>
18 <li><a href="#knownproblems">Known Problems</a>
19 <li><a href="#additionalinfo">Additional Information</a></li>
22 <div class="doc_author">
23 <p>Written by the <a href="http://llvm.cs.uiuc.edu">LLVM Team</a><p>
26 <!-- *********************************************************************** -->
27 <div class="doc_section">
28 <a name="intro">Introduction</a>
30 <!-- *********************************************************************** -->
32 <div class="doc_text">
34 <p>This document contains the release notes for the LLVM compiler
35 infrastructure, release 1.5. Here we describe the status of LLVM, including any
36 known problems and major improvements from the previous release. The most
37 up-to-date version of this document can be found on the <a
38 href="http://llvm.cs.uiuc.edu/releases/1.5/">LLVM 1.5 web site</a>. If you are
39 not reading this on the LLVM web pages, you should probably go there because
40 this document may be updated after the release.</p>
42 <p>For more information about LLVM, including information about the latest
43 release, please check out the <a href="http://llvm.cs.uiuc.edu">main LLVM
44 web site</a>. If you have questions or comments, the <a
45 href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
46 list</a> is a good place to send them.</p>
48 <p>Note that if you are reading this file from CVS or the main LLVM web page,
49 this document applies to the <i>next</i> release, not the current one. To see
50 the release notes for the current or previous releases, see the <a
51 href="http://llvm.cs.uiuc.edu/releases/">releases page</a>.</p>
55 <!-- *********************************************************************** -->
56 <div class="doc_section">
57 <a name="whatsnew">What's New?</a>
59 <!-- *********************************************************************** -->
61 <div class="doc_text">
63 <p>This is the sixth public release of the LLVM Compiler Infrastructure.</p>
65 <p> At this time, LLVM is known to correctly compile a wide range of C and C++
66 programs, including the SPEC CPU95 & 2000 suite. It includes bug fixes for
67 those problems found since the 1.4 release and a large number of new features
68 and enhancements, described below.</p>
72 <!--=========================================================================-->
73 <div class="doc_subsection">
74 <a name="newfeatures">New Features in LLVM 1.5</a>
77 <!--_________________________________________________________________________-->
78 <div class="doc_subsubsection"><a name="newcg">New Native Code
81 <div class="doc_text">
83 This release includes new native code generators for <a
84 href="#alpha-be">Alpha</a>, <a href="#ia64-be">IA-64</a>, and <a
85 href="#sparcv8">SPARC-V8</a> (32-bit SPARC). These code generators are still
86 beta quality, but are progressing rapidly. The Alpha backend is implemented
87 with an eye towards being compatible with the widely used SimpleScalar
92 <!--_________________________________________________________________________-->
93 <div class="doc_subsubsection"><a name="selectiondag">New Instruction
94 Selector Framework</a></div>
96 <div class="doc_text">
97 <p>This release includes a <a href="CodeGenerator.html#instselect">new framework
98 for building instruction selectors</a>, which has long been the hardest part of
99 building a new LLVM target. This framework handles a lot of the mundane (but
100 easy to get wrong) details of writing the instruction selector, such as
101 generating efficient code for <a
102 href="LangRef.html#i_getelementptr">getelementptr</a> instructions, promoting
103 small integer types to larger types (e.g. for RISC targets with one size of
104 integer registers), expanding 64-bit integer operations for 32-bit hosts, etc.
105 Currently, the X86, PowerPC, Alpha, and IA-64 backends use this framework. The
106 SPARC backends will be migrated when time permits.
110 <!--_________________________________________________________________________-->
111 <div class="doc_subsubsection"><a name="customccs">New Support for Per-Function
112 Calling Conventions</a></div>
114 <div class="doc_text">
115 <p>LLVM 1.5 adds supports for <a href="LangRef.html#callingconv">per-function
116 calling conventions</a>. Traditionally, the LLVM code generators match the
117 native C calling conventions for a target. This is important for compatibility,
118 but is not very flexible. This release allows custom calling conventions to be
119 established for functions, and defines three target-independent conventions (<a
120 href="LangRef.html#callingconv">C call, fast call, and cold call</a>) which may
121 be supported by code generators. When possible, the LLVM optimizer promotes C
122 functions to use the "fastcc" convention, allowing the use of more efficient
123 calling sequences (e.g., parameters are passed in registers in the X86 target).
126 <p>Targets may now also define target-specific calling conventions, allowing
127 LLVM to fully support calling convention altering options (e.g. GCC's
128 <tt>-mregparm</tt> flag) and well-defined target conventions (e.g. stdcall and
129 fastcall on X86).</p>
132 <!--_________________________________________________________________________-->
133 <div class="doc_subsubsection"><a name="tailcalls">New Support for
134 Proper Tail Calls</a></div>
136 <div class="doc_text">
137 <p>The release now includes support for <a
138 href="http://doi.acm.org/10.1145/277650.277719">proper tail calls</a>, as
139 required to implement languages like Scheme. Tail calls make use of two
140 features: custom calling conventions (described above), which allow the code
141 generator to emit code for the caller to deallocate its own stack when it
142 returns. The second feature is a flag on the <a href="LangRef.html#i_call">call
143 instruction</a>, which indicates that the callee does not access the caller's
144 stack frame (indicating that it is acceptable to deallocate the caller stack
145 before invoking the callee). LLVM proper tail calls run on the system stack (as
146 do normal calls), supports indirect tail calls, tail calls with arbitrary
147 numbers of arguments, tail calls where the callee requires more argument space
148 than the caller, etc. The only case not supported are varargs calls, but that
149 could be added if desired.
152 <p>In order for a front-end to get guaranteed tail call, it must mark functions
153 as "fastcc", mark calls with the 'tail' marker, and follow the call with a
154 return of the called value (or void). The optimizer and code generator attempt
155 to handle more general cases, but the simple case will always work if the code
156 generator supports tail calls. Here is a simple example:</p>
159 fastcc int %bar(int %X, int(double, int)* %FP) { ;<i> fastcc</i>
160 %Y = tail call fastcc int %FP(double 0.0, int %X) ;<i> tail, fastcc</i>
165 <p>In LLVM 1.5, the X86 code generator is the only target that has been enhanced
166 to support proper tail calls (other targets will be enhanced in future).
167 Further, because this support was added very close to the release, it is
168 disabled by default. Pass <tt>-enable-x86-fastcc</tt> to llc to enable it (this
169 will be enabled by default in the next release). The example above compiles to:
174 sub ESP, 8 # Callee uses more space than the caller
175 mov ECX, DWORD PTR [ESP + 8] # Get the old return address
176 mov DWORD PTR [ESP + 4], 0 # First half of 0.0
177 mov DWORD PTR [ESP + 8], 0 # Second half of 0.0
178 mov DWORD PTR [ESP], ECX # Put the return address where it belongs
179 jmp EDX # Tail call "FP"
183 With fastcc on X86, the first two integer arguments are passed in EAX/EDX, the
184 callee pops its arguments off the stack, and the argument area is always a
185 multiple of 8 bytes in size.
190 <!--_________________________________________________________________________-->
191 <div class="doc_subsubsection">Other New Features</div>
193 <div class="doc_text">
195 <li>LLVM now includes an <a href="http://llvm.cs.uiuc.edu/PR415">
196 Interprocedural Sparse Conditional Constant Propagation</a> pass, named
197 -ipsccp, which is run by default at link-time.</li>
198 <li>LLVM 1.5 is now about 15% faster than LLVM 1.4 and its core data
199 structures use about 30% less memory.</li>
200 <li>Support for Microsoft Visual Studio is improved, and <a
201 href="GettingStartedVS.html">now documented</a>.</li>
202 <li><a href="GettingStarted.html#config">Configuring LLVM to build a subset
203 of the available targets</a> is now implemented, via the
204 <tt>--enable-targets=</tt> option.</li>
205 <li>LLVM can now create native shared libraries with '<tt>llvm-gcc ...
206 -shared -Wl,-native</tt>' (or with <tt>-Wl,-native-cbe</tt>).</li>
207 <li>LLVM now supports a new "<a href="LangRef.html#i_prefetch">llvm.prefetch
208 </a>" intrinsic, and llvm-gcc now supports __builtin_prefetch.
209 <li>LLVM now supports intrinsics for <a href="LangRef.html#int_count">bit
210 counting</a> and llvm-gcc now implements the GCC
211 <tt>__builtin_popcount</tt>, <tt>__builtin_ctz</tt>, and
212 <tt>__builtin_clz</tt> builtins.</li>
213 <li>LLVM now mostly builds on HP-UX with the HP aCC Compiler.</li>
214 <li>The LLVM X86 backend can now emit Cygwin-compatible .s files.</li>
215 <li>LLVM now includes workarounds in the code generator generator which
216 reduces the likelyhood of <a href="http://llvm.cs.uiuc.edu/PR448">GCC
217 hitting swap during optimized builds</a>.</li>
218 <li>The PowerPC backend generates far better code than in LLVM 1.4.</li>
222 <!--=========================================================================-->
223 <div class="doc_subsection">
224 <a name="codequality">Code Quality Improvements in LLVM 1.5</a>
227 <div class="doc_text">
229 <li>The -globalopt pass now promotes non-address-taken static globals that are
230 only accessed in main to SSA registers.</li>
232 <li>The new -simplify-libcalls pass improves code generated for well-known
233 library calls. The pass optimizes calls to many of the string, memory, and
234 standard I/O functions (e.g. replace the calls with simpler/faster calls) when
235 possible, given information known statically about the arguments to the call.
238 <li>Loops with trip counts based on array pointer comparisons (e.g. "<tt>for (i
239 = 0; &A[i] != &A[100]; ++i) ...</tt>") are optimized better than before,
240 which primarily helps iterator-intensive C++ codes.</li>
242 <li>The code generator now can provide and use information about commutative
243 two-address instructions when performing register allocation.</li>
245 <li>The optimizer now eliminates simple cases where redundant conditions exist
246 between neighboring blocks.</li>
248 <li>The reassociation pass (which turns (1+X+3) into (X+1+3) among other
249 things), is more aggressive an intelligent.</li>
254 <!--=========================================================================-->
255 <div class="doc_subsection">
256 <a name="bugfix">Significant Bugs Fixed in LLVM 1.5</a>
259 <div class="doc_text">
262 <p>Bugs fixed in the LLVM Core:</p>
264 <li><a href="http://llvm.cs.uiuc.edu/PR491">[dse] DSE deletes stores that
265 are partially overwritten by smaller stores</a></li>
266 <li><a href="http://llvm.cs.uiuc.edu/PR548">[instcombine] miscompilation of
267 setcc or setcc in one case</a></li>
268 <li>Transition code for LLVM 1.0 style varargs was removed from the .ll file
269 parser. LLVM 1.0 bytecode files are still supported. </li>
272 <p>Code Generator Bugs:</p>
274 <li><a href="http://llvm.cs.uiuc.edu/PR490">[cbackend] Logical constant
275 expressions (and/or/xor) not implemented</a>.</li>
276 <li><a href="http://llvm.cs.uiuc.edu/PR511">[cbackend] C backend does not
277 respect 'volatile'</a>.</li>
278 <li>The JIT sometimes miscompiled globals and constant pool entries for
279 64-bit integer constants on 32-bit hosts.</li>
282 <p>Bugs in the C/C++ front-end:</p>
284 <li><a href="http://llvm.cs.uiuc.edu/PR487">[llvmgcc] llvm-gcc incorrectly
285 rejects some constant initializers involving the addresses of array
287 <li><a href="http://llvm.cs.uiuc.edu/PR501">[llvm-g++] Crash compiling
288 anonymous union</a></li>
289 <li><a href="http://llvm.cs.uiuc.edu/PR509">[llvm-g++] Do not use dynamic
290 initialization where static init will do</a></li>
291 <li><a href="http://llvm.cs.uiuc.edu/PR510">[llvmgcc] Field offset
292 miscalculated for some structure fields following bit fields</a></li>
293 <li><a href="http://llvm.cs.uiuc.edu/PR513">[llvm-g++] Temporary lifetimes
294 incorrect for short circuit logical operations</a></li>
295 <li><a href="http://llvm.cs.uiuc.edu/PR517">[llvm-gcc] Crash compiling
296 bitfield <-> aggregate assignment</a></li>
297 <li><a href="http://llvm.cs.uiuc.edu/PR520">[llvm-g++] Error compiling
298 virtual function thunk with an unnamed argument</a></li>
299 <li><a href="http://llvm.cs.uiuc.edu/PR522">[llvm-gcc] Crash on certain
300 C99 complex number routines</a></li>
301 <li><a href="http://llvm.cs.uiuc.edu/PR529">[llvm-g++] Crash using placement
302 new on an array type</a></li>
307 <!-- *********************************************************************** -->
308 <div class="doc_section">
309 <a name="portability">Portability and Supported Platforms</a>
311 <!-- *********************************************************************** -->
313 <div class="doc_text">
315 <p>LLVM is known to work on the following platforms:</p>
318 <li>Intel and AMD machines running Red Hat Linux and FreeBSD (and probably
319 other unix-like systems).</li>
320 <li>Sun UltraSPARC workstations running Solaris 8.</li>
321 <li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
322 support is available for native builds with Visual C++).</li>
323 <li>PowerPC-based Mac OS X systems, running 10.2 and above.</li>
324 <li>Alpha-based machines running Debian GNU/Linux.</li>
325 <li>Itanium-based machines running Linux and HP-UX.</li>
328 <p>The core LLVM infrastructure uses
329 <a href="http://www.gnu.org/software/autoconf/">GNU autoconf</a> to adapt itself
330 to the machine and operating system on which it is built. However, minor
331 porting may be required to get LLVM to work on new platforms. We welcome your
332 portability patches and reports of successful builds or error messages.</p>
336 <!-- *********************************************************************** -->
337 <div class="doc_section">
338 <a name="knownproblems">Known Problems</a>
340 <!-- *********************************************************************** -->
342 <div class="doc_text">
344 <p>This section contains all known problems with the LLVM system, listed by
345 component. As new problems are discovered, they will be added to these
346 sections. If you run into a problem, please check the <a
347 href="http://llvm.cs.uiuc.edu/bugs/">LLVM bug database</a> and submit a bug if
348 there isn't already one.</p>
352 <!-- ======================================================================= -->
353 <div class="doc_subsection">
354 <a name="experimental">Experimental features included with this release</a>
357 <div class="doc_text">
359 <p>The following components of this LLVM release are either untested, known to
360 be broken or unreliable, or are in early development. These components should
361 not be relied on, and bugs should not be filed against them, but they may be
362 useful to some people. In particular, if you would like to work on one of these
363 components, please contact us on the llvmdev list.</p>
366 <li>The following passes are incomplete or buggy, and may be removed in future
367 releases: <tt>-cee, -branch-combine, -instloops, -paths, -pre</tt></li>
368 <li>The <tt>llvm-db</tt> tool is in a very early stage of development, but can
369 be used to step through programs and inspect the stack.</li>
370 <li>The "iterative scan" register allocator (enabled with
371 <tt>-regalloc=iterativescan</tt>) is not stable.</li>
372 <li>The SparcV8, Alpha, and IA64 code generators are experimental.</li>
377 <!-- ======================================================================= -->
378 <div class="doc_subsection">
379 <a name="core">Known problems with the LLVM Core</a>
382 <div class="doc_text">
385 <li>In the JIT, <tt>dlsym()</tt> on a symbol compiled by the JIT will not
387 <li>The JIT does not use mutexes to protect its internal data structures. As
388 such, execution of a threaded program could cause these data structures to be
391 <li><a href="http://llvm.cs.uiuc.edu/PR240">The lower-invoke pass does not
392 mark values live across a setjmp as volatile</a>. This missing feature
393 only affects targets whose setjmp/longjmp libraries do not save and restore
394 the entire register file.</li>
398 <!-- ======================================================================= -->
399 <div class="doc_subsection">
400 <a name="c-fe">Known problems with the C front-end</a>
403 <!-- _______________________________________________________________________ -->
404 <div class="doc_subsubsection">Bugs</div>
406 <div class="doc_text">
408 <li>C99 Variable sized arrays do not release stack memory when they go out of
409 scope. Thus, the following program may run out of stack space:
411 for (i = 0; i != 1000000; ++i) {
417 <li>Initialization of global union variables can only be done <a
418 href="http://llvm.cs.uiuc.edu/PR162">with the largest union member</a>.</li>
423 <!-- _______________________________________________________________________ -->
424 <div class="doc_subsubsection">
428 <div class="doc_text">
432 <li>Inline assembly is not yet supported.</li>
434 <li>"long double" is transformed by the front-end into "double". There is no
435 support for floating point data types of any size other than 32 and 64
438 <li>The following Unix system functionality has not been tested and may not
441 <li><tt>sigsetjmp</tt>, <tt>siglongjmp</tt> - These are not turned into the
442 appropriate <tt>invoke</tt>/<tt>unwind</tt> instructions. Note that
443 <tt>setjmp</tt> and <tt>longjmp</tt> <em>are</em> compiled correctly.
444 <li><tt>getcontext</tt>, <tt>setcontext</tt>, <tt>makecontext</tt>
445 - These functions have not been tested.
448 <li>Although many GCC extensions are supported, some are not. In particular,
449 the following extensions are known to <b>not be</b> supported:
451 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
452 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html#Nested%20Functions">Nested Functions</a>: As in Algol and Pascal, lexical scoping of functions.</li>
453 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</li>
454 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Extended%20Asm">Extended Asm</a>: Assembler instructions with C expressions as operands.</li>
455 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
456 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Asm-Labels.html#Asm%20Labels">Asm Labels</a>: Specifying the assembler name to use for a C symbol.</li>
457 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Explicit-Reg-Vars.html#Explicit%20Reg%20Vars">Explicit Reg Vars</a>: Defining variables residing in specified registers.</li>
458 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html#Vector%20Extensions">Vector Extensions</a>: Using vector instructions through built-in functions.</li>
459 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Target-Builtins.html#Target%20Builtins">Target Builtins</a>: Built-in functions specific to particular targets.</li>
460 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread_002dLocal.html">Thread-Local</a>: Per-thread variables.</li>
461 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
464 <p>The following GCC extensions are <b>partially</b> supported. An ignored
465 attribute means that the LLVM compiler ignores the presence of the attribute,
466 but the code should still work. An unsupported attribute is one which is
467 ignored by the LLVM compiler and will cause a different interpretation of
471 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
472 Arrays whose length is computed at run time.<br>
473 Supported, but allocated stack space is not freed until the function returns (noted above).</li>
475 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>:
477 Declaring that functions have no side effects or that they can never
480 <b>Supported:</b> <tt>format</tt>, <tt>format_arg</tt>, <tt>non_null</tt>,
481 <tt>noreturn</tt>, <tt>constructor</tt>, <tt>destructor</tt>,
483 <tt>deprecated</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
485 <b>Ignored:</b> <tt>noinline</tt>,
486 <tt>always_inline</tt>, <tt>pure</tt>, <tt>const</tt>, <tt>nothrow</tt>,
487 <tt>malloc</tt>, <tt>no_instrument_function</tt>, <tt>cdecl</tt><br>
489 <b>Unsupported:</b> <tt>used</tt>, <tt>section</tt>, <tt>alias</tt>,
490 <tt>visibility</tt>, <tt>regparm</tt>, <tt>stdcall</tt>,
491 <tt>fastcall</tt>, all other target specific attributes</li>
493 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
494 Specifying attributes of variables.<br>
495 <b>Supported:</b> <tt>cleanup</tt>, <tt>common</tt>, <tt>nocommon</tt>,
496 <tt>deprecated</tt>, <tt>transparent_union</tt>,
497 <tt>unused</tt>, <tt>weak</tt><br>
499 <b>Unsupported:</b> <tt>aligned</tt>, <tt>mode</tt>, <tt>packed</tt>,
500 <tt>section</tt>, <tt>shared</tt>, <tt>tls_model</tt>,
501 <tt>vector_size</tt>, <tt>dllimport</tt>,
502 <tt>dllexport</tt>, all target specific attributes.</li>
504 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>: Specifying attributes of types.<br>
505 <b>Supported:</b> <tt>transparent_union</tt>, <tt>unused</tt>,
506 <tt>deprecated</tt>, <tt>may_alias</tt><br>
508 <b>Unsupported:</b> <tt>aligned</tt>, <tt>packed</tt>,
509 all target specific attributes.</li>
511 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
512 Other built-in functions.<br>
513 We support all builtins which have a C language equivalent (e.g.,
514 <tt>__builtin_cos</tt>), <tt>__builtin_alloca</tt>,
515 <tt>__builtin_types_compatible_p</tt>, <tt>__builtin_choose_expr</tt>,
516 <tt>__builtin_constant_p</tt>, and <tt>__builtin_expect</tt>
517 (currently ignored). We also support builtins for ISO C99 floating
518 point comparison macros (e.g., <tt>__builtin_islessequal</tt>),
519 <tt>__builtin_prefetch</tt>, <tt>__builtin_popcount[ll]</tt>,
520 <tt>__builtin_clz[ll]</tt>, and <tt>__builtin_ctz[ll]</tt>.</li>
523 <p>The following extensions <b>are</b> known to be supported:</p>
526 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html#Labels%20as%20Values">Labels as Values</a>: Getting pointers to labels and computed gotos.</li>
527 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>: Putting statements and declarations inside expressions.</li>
528 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Typeof.html#Typeof">Typeof</a>: <code>typeof</code>: referring to the type of an expression.</li>
529 <li><a href="http://gcc.gnu.org/onlinedocs/gcc-3.4.0/gcc/Lvalues.html#Lvalues">Lvalues</a>: Using <code>?:</code>, "<code>,</code>" and casts in lvalues.</li>
530 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals">Conditionals</a>: Omitting the middle operand of a <code>?:</code> expression.</li>
531 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long%20Long">Long Long</a>: Double-word integers.</li>
532 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex">Complex</a>: Data types for complex numbers.</li>
533 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex%20Floats">Hex Floats</a>:Hexadecimal floating-point constants.</li>
534 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero%20Length">Zero Length</a>: Zero-length arrays.</li>
535 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li>
536 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variadic-Macros.html#Variadic%20Macros">Variadic Macros</a>: Macros with a variable number of arguments.</li>
537 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>: Slightly looser rules for escaped newlines.</li>
538 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Subscripting.html#Subscripting">Subscripting</a>: Any array can be subscripted, even if not an lvalue.</li>
539 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html#Pointer%20Arith">Pointer Arith</a>: Arithmetic on <code>void</code>-pointers and function pointers.</li>
540 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li>
541 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound%20Literals">Compound Literals</a>: Compound literals give structures, unions,
542 or arrays as values.</li>
543 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated%20Inits">Designated Inits</a>: Labeling elements of initializers.</li>
544 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Cast-to-Union.html#Cast%20to%20Union">Cast to Union</a>: Casting to union type from any member of the union.</li>
545 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case%20Ranges">Case Ranges</a>: `case 1 ... 9' and such.</li>
546 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html#Mixed%20Declarations">Mixed Declarations</a>: Mixing declarations and code.</li>
547 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Prototypes.html#Function%20Prototypes">Function Prototypes</a>: Prototype declarations and old-style definitions.</li>
548 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Comments.html#C_002b_002b-Comments">C++ Comments</a>: C++ comments are recognized.</li>
549 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar%20Signs">Dollar Signs</a>: Dollar sign is allowed in identifiers.</li>
550 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Character-Escapes.html#Character%20Escapes">Character Escapes</a>: <code>\e</code> stands for the character <ESC>.</li>
551 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment">Alignment</a>: Inquiring about the alignment of a type or variable.</li>
552 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline">Inline</a>: Defining inline functions (as fast as macros).</li>
553 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alternate-Keywords.html#Alternate%20Keywords">Alternate Keywords</a>:<code>__const__</code>, <code>__asm__</code>, etc., for header files.</li>
554 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Incomplete-Enums.html#Incomplete%20Enums">Incomplete Enums</a>: <code>enum foo;</code>, with details to follow.</li>
555 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Names.html#Function%20Names">Function Names</a>: Printable strings which are the name of the current function.</li>
556 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Return-Address.html#Return%20Address">Return Address</a>: Getting the return or frame address of a function.</li>
557 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html#Unnamed%20Fields">Unnamed Fields</a>: Unnamed struct/union fields within structs/unions.</li>
558 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute%20Syntax">Attribute Syntax</a>: Formal syntax for attributes.</li>
563 <p>If you run into GCC extensions which have not been included in any of these
564 lists, please let us know (also including whether or not they work).</p>
568 <!-- ======================================================================= -->
569 <div class="doc_subsection">
570 <a name="c++-fe">Known problems with the C++ front-end</a>
573 <div class="doc_text">
575 <p>For this release, the C++ front-end is considered to be fully
576 tested and works for a number of non-trivial programs, including LLVM
581 <!-- _______________________________________________________________________ -->
582 <div class="doc_subsubsection">Bugs</div>
584 <div class="doc_text">
587 <li>The C++ front-end inherits all problems afflicting the <a href="#c-fe">C
590 <li><b>IA-64 specific</b>: The C++ front-end does not use <a
591 href="http://llvm.cs.uiuc.edu/PR406">IA64 ABI compliant layout of v-tables</a>.
592 In particular, it just stores function pointers instead of function
593 descriptors in the vtable. This bug prevents mixing C++ code compiled with
594 LLVM with C++ objects compiled by other C++ compilers.</li>
600 <!-- _______________________________________________________________________ -->
601 <div class="doc_subsubsection">
605 <div class="doc_text">
609 <li>The C++ front-end is based on a pre-release of the GCC 3.4 C++ parser. This
610 parser is significantly more standards compliant (and picky) than prior GCC
611 versions. For more information, see the C++ section of the <a
612 href="http://gcc.gnu.org/gcc-3.4/changes.html">GCC 3.4 release notes</a>.</li>
614 <li>Destructors for local objects are not always run when a <tt>longjmp</tt> is
615 performed. In particular, destructors for objects in the <tt>longjmp</tt>ing
616 function and in the <tt>setjmp</tt> receiver function may not be run.
617 Objects in intervening stack frames will be destroyed, however (which is
618 better than most compilers).</li>
620 <li>The LLVM C++ front-end follows the <a
621 href="http://www.codesourcery.com/cxx-abi">Itanium C++ ABI</a>.
622 This document, which is not Itanium specific, specifies a standard for name
623 mangling, class layout, v-table layout, RTTI formats, and other C++
624 representation issues. Because we use this API, code generated by the LLVM
625 compilers should be binary compatible with machine code generated by other
626 Itanium ABI C++ compilers (such as G++, the Intel and HP compilers, etc).
627 <i>However</i>, the exception handling mechanism used by LLVM is very
628 different from the model used in the Itanium ABI, so <b>exceptions will not
629 interact correctly</b>. </li>
635 <!-- ======================================================================= -->
636 <div class="doc_subsection">
637 <a name="x86-be">Known problems with the X86 back-end</a>
640 <div class="doc_text">
648 <!-- ======================================================================= -->
649 <div class="doc_subsection">
650 <a name="sparcv9-be">Known problems with the SparcV9 back-end</a>
653 <div class="doc_text">
656 <li><a href="http://llvm.cs.uiuc.edu/PR60">[sparcv9] SparcV9 backend miscompiles
657 several programs in the LLVM test suite</a></li>
662 <!-- ======================================================================= -->
663 <div class="doc_subsection">
664 <a name="ppc-be">Known problems with the PowerPC back-end</a>
667 <div class="doc_text">
675 <!-- ======================================================================= -->
676 <div class="doc_subsection">
677 <a name="c-be">Known problems with the C back-end</a>
680 <div class="doc_text">
684 <li>The C back-end produces code that violates the ANSI C Type-Based Alias
685 Analysis rules. As such, special options may be necessary to compile the code
686 (for example, GCC requires the <tt>-fno-strict-aliasing</tt> option). This
687 problem probably cannot be fixed.</li>
689 <li><a href="http://llvm.cs.uiuc.edu/PR56">Zero arg vararg functions are not
690 supported</a>. This should not affect LLVM produced by the C or C++
697 <!-- ======================================================================= -->
698 <div class="doc_subsection">
699 <a name="alpha-be">Known problems with the Alpha back-end</a>
702 <div class="doc_text">
706 <li>On 21164s, some rare FP arithmatic sequences which may trap do not have the appropriate nops inserted to ensure restartability.</li>
708 <li>Vararg functions are not supported.</li>
710 <li>Due to the vararg problems, C++ exceptions do not work. Small changes are required to the CFE (which break correctness in the exception handler) to compile the exception handling library (and thus the C++ standard library).</li>
716 <!-- ======================================================================= -->
717 <div class="doc_subsection">
718 <a name="ia64-be">Known problems with the IA64 back-end</a>
721 <div class="doc_text">
725 <li>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> are
726 made where the argument is not 16-byte aligned, as required on IA64. (Strictly
727 speaking this is not a bug in the IA64 back-end; it will also be encountered
728 when building C++ programs using the C back-end.)</li>
730 <li>There are a few ABI violations which will lead to problems
731 when mixing LLVM output with code built with other compilers,
732 particularly for C++ and floating-point programs.</li>
734 <li>Vararg functions are not supported.</li>
740 <!-- ======================================================================= -->
741 <div class="doc_subsection">
742 <a name="sparcv8">Known problems with the SPARC-V8 back-end</a>
745 <div class="doc_text">
748 <li>Many features are still missing (e.g. support for 64-bit integer
751 <li>This backend needs to be updated to use the SelectionDAG instruction
752 selection framework.</li>
757 <!-- *********************************************************************** -->
758 <div class="doc_section">
759 <a name="additionalinfo">Additional Information</a>
761 <!-- *********************************************************************** -->
763 <div class="doc_text">
765 <p>A wide variety of additional information is available on the LLVM web page,
766 including <a href="http://llvm.cs.uiuc.edu/docs/#maillist">mailing lists</a> and
767 <a href="http://llvm.cs.uiuc.edu/pubs/">publications describing algorithms and
768 components implemented in LLVM</a>. The web page also contains versions of the
769 API documentation which is up-to-date with the CVS version of the source code.
770 You can access versions of these documents specific to this release by going
771 into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
773 <p>If you have any questions or comments about LLVM, please feel free to contact
774 us via the <a href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">mailing
779 <!-- *********************************************************************** -->
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